1. Field of the Invention
The subject invention generally pertains to controls that may need to receive a broad range of input voltages (e.g., 110 to 220 VAC), as is often the case with systems pertaining to HVAC (heating, ventilating, and air conditioning), and the invention more specifically pertains to converting the broad range of input voltages to control signals of much lower voltage (e.g., 0 to 5 volts).
2. Description of Related Art
Electronic controls of commercial and industrial HVAC systems often need to receive and interpret input voltage signals that can range from a nominal 110 to 220 VAC. Typically, 110 volts is used in the United States, while 220 volts is more common in other countries. However, many controls need to handle both 110 and 220 volts.
The relatively high input voltages typically come from sensing the condition of various HVAC devices such as motor starters, contactors, relays, limit switches, flow switches for evaporator and condenser pumps, pressure switches for condenser shells, motor winding thermostats, electric heaters, etc. The input voltage signals provide the control with feedback on the operating condition or status of the HVAC system. In response to the feedback, the control may simply monitor the HVAC system or provide various output signals that adjust or vary the system""s operation.
Such controls often include a microprocessor for analyzing the input and providing logical output responses to the HVAC system. Since many microprocessors operate on a binary system using voltage signals of no more than about five volts, the 110/220-volt inputs need to be reduced before they reach the microprocessor.
After reducing the input voltages to about 5 volts, the lower voltages are preferably electrically isolated from the higher voltages. The electrical isolation helps protect the microprocessor and its associated low-voltage components from being damaged by the higher voltages. Also, when troubleshooting a low-voltage portion of the control, electrical isolation helps protect a service technician from being accidentally shocked by higher voltages. Lastly, for UL approval, Underwriters Laboratories, Inc. requires electrical isolation between electrical lines of significantly different voltages.
Today, step-down transformers are often used for electrical isolation. However, transformers have several disadvantages. If a transformer reduces an input signal from 220 to five volts, that same transformer could reduce a 110-volt signal to an unacceptably low 2.5 volts. Thus, separate transformers are usually needed to handle both 110 and 220-volt inputs. A transformer""s bulk also makes them generally incompatible with compact circuit boards using surface-mount technology. Moreover, micro-transformers have rather delicate wire for its windings, which tends to reduce the reliability and durability of such transformers.
Optical isolators are also often used for electrical isolation. An optical isolator typically turns on when an input voltage reaches a certain threshold, and otherwise turns off (with some hysteresis between its on and off states). The threshold is generally a fixed value that is dependent on other electrical components associated with the optical isolator. If the electrical characteristics of the optical isolator or its other related components vary due to their manufacturing tolerances, the threshold may vary accordingly. This can become a critical problem when an input voltage is at or very near the threshold.
For example, if an input voltage is just barely below the threshold, the input may be interpreted as a logic-0, i.e., turned off, when actually the input might be just a weak signal that should be interpreted as a logic-1.
Moreover, electrical isolation circuits employing optical isolators are typically designed to handle a generally narrow range of input voltages. Otherwise, such circuits may generate a significant amount of heat when receiving higher voltage signals.
Voltage spikes, electrical noise, and other electrical transients may falsely trip an optical isolator. Although high-frequency filters and other circuitry can be used to block most false signals, it can be difficult to provide a circuit that can anticipate and reject every imaginable form of electrical noise.
In order to receive and interpret a broad range of input voltages, a control translates the input voltage to a pulsating voltage whose number of pulses varies with the voltage amplitude of the input. The control includes an analog, digital, and/or software component that interprets the pulsating voltage to determine the value of the input voltage. The input""s value may be the actual amplitude of the voltage or may simply be a binary value, such as a logic-0 or logic-1, which respectively represents the absence or presence of the input voltage.
In some embodiments, it is an object of the invention to determine the value of the input voltage by counting the pulses of the pulsating voltage.
In some embodiments, it is an object of the invention to determine the value of the input voltage by accumulating the pulsating voltage across a capacitor and then measuring the voltage across the capacitor.
In some embodiments, it is an object of the invention to determine the value of the input voltage by applying software logic in interpreting a count or an analog accumulation of the pulsating voltage.
In some embodiments, the software provides certain time-delays and/or hysteresis that filter out electrical noise or erroneous electrical spikes, thus avoiding misinterpreting an input.
Another object of the invention is to provide software-based hysteresis from logic-1 to logic-0 values and vice versa.
In some embodiments, it is an object of the invention to electrically isolate a lower voltage portion of the control from the higher voltage input, without having to rely on an isolation transformer.
Another object of the invention is to employ an optical isolator that electrically isolates one pulsating signal from another pulsating signal.
Another object is to take multiple count readings of pulses that indicate a voltage amplitude to avoid false readings based on a single count.
A further object of the invention is to provide a control that can receive and interpret both 110 and 220-volt inputs.
A still further object of the invention is to provide a high-resolution method of sensing a voltage by converting the voltage to a series of pulses whose number of pulses increases with the amplitude of the voltage, whereby increasing the number of pulses for a given voltage increases the resolution accordingly.
Another object is to provide a method of reliably interpreting an input using electrical components of standard tolerance.
Another object is to take full advantage of surface-mount technology by not using a transformer.
The present invention provides a control adapted to monitor an operating status of a system in response to receiving an input voltage having an input voltage amplitude and a nominal frequency. The control includes an input terminal adapted to receive the input voltage, and a first pulse circuit coupled to the input terminal and adapted to generate a first pulsating voltage having a first frequency that varies as a function of the input voltage amplitude the first frequency is at least as great as the nominal frequency when the input voltage amplitude is above an upper limit. The control also includes a second pulse circuit adapted to generate a plurality of pulses in response to the first pulsating voltage, an electrical isolator that helps isolate the plurality of pulses from the input voltage; and a logic circuit coupled to the second pulse circuit. The logic circuit selectively creates a first binary value in response to the plurality of pulses indicating the input voltage amplitude is above the upper limit and creates an opposite binary value in response to the plurality of pulses indicating the input voltage amplitude is below a lower limit. The first binary value and the opposite binary value at least partially provide an indication of the operating status of the system.
The present invention also provides a method of measuring an input voltage amplitude of an input voltage having a nominal frequency. The method comprises the steps of: sensing the input voltage; generating a pulsating voltage having a generated frequency that varies as a function of the input voltage amplitude; generating a plurality of pulses that vary as a function of the generated frequency; and counting the plurality of pulses to determine the input voltage amplitude.
The present invention additionally provides a method of interpreting an input voltage having a input voltage amplitude and a nominal frequency. The method includes: sensing the input voltage; generating a pulsating voltage having a generated frequency that varies as a function of the input voltage amplitude; generating a plurality of pulses that varies as a function of the generated frequency; and creating a first digital value based on the plurality of pulses, whereby the first digital value indicates that the input voltage amplitude has reached a certain value.
The present invention further provides a control suitable for an HVAC system that conditions the air of a comfort zone. The control is adapted to monitor an operating status of the HVAC system in response to receiving an input voltage having an input voltage amplitude and a nominal frequency. The control comprises an input terminal adapted to receive the input voltage, and a first pulse circuit coupled to the input terminal and adapted to generate a first pulsating voltage having a first frequency that varies as a function of the input voltage amplitude with the first frequency being at least as great as the nominal frequency when the input voltage amplitude is above an upper limit. The control also comprises a second pulse circuit adapted to generate a plurality of pulses in response to the first pulsating voltage, an electrical isolator that helps isolate the plurality of pulses from said input voltage; and a logic circuit coupled to the second pulse circuit. The logic circuit selectively creates a first binary value in response to the plurality of pulses indicating the input voltage amplitude is above the upper limit and creates an opposite binary value in response to the plurality of pulses indicating the input voltage amplitude is below a lower limit. The first binary value and the opposite binary value at least partially provide an indication of the operating status of the HVAC system.